1. Field of the Invention
The present invention relates to a supply pump for a common rail type (accumulation type) fuel injection system used in a diesel engine having a plurality of cylinders.
2. Description of the Related Art
There is a demand for high pressure fuel injection, and common rail fuel injection systems are developed in recent years. A general idea of a common rail fuel injection system will be described in reference to FIG. 2 of the accompanying drawings. A conventional common rail fuel injection system 1 includes a supply pump 2, a common rail 3 and unit injectors 4. The supply pump 2 feeds a pressurized fuel to the common rail 3. The pressurized fuel is accumulated in the common rail 3 and injected to cylinders of an engine from the respective unit injectors 4. Timing and amount of fuel injection from the unit injectors 4 are controlled by ECU (not shown).
Referring to FIG. 2A, the supply pump 2 is operatively connected to a crankshaft 78 of the engine 86 via a power transmission mechanism 84 so that it is driven by the engine 86. A typical power transmission mechanism is a chain-and-sprocket mechanism, a belt-and-pulley mechanism or a gear train mechanism.
The supply pump 2 also has a valve for adjusting a flow rate of pressurized fuel, and ECU controls this valve such that a discharge pressure of the supply pump 2 becomes a desired common rail pressure.
The common rail pressure drops each time a fuel is injected to the cylinders of the engine 86. In order to maintain the common rail pressure to a particular value or range, a fuel delivery timing of the supply pump 2 is synchronized with a fuel injection timing of the unit injectors 4 in the conventional common rail fuel injection system 1. The fuel delivery from the supply pump 2 takes place each time the fuel injection to the engine 86 takes place. Such a fuel injection system is disclosed in, for example, Japanese Patent Application, Kokai No. 4-308355.
However, the common rail fuel injection system 1 is different from a general fuel injection system in that the fuel delivery does not directly influence the fuel injection. Thus, the supply pump 2 does not necessarily feed the pressurized fuel to the common rail 3 each time the fuel is injected to the engine 86.
For example, if the engine has six cylinders, the fuel injection takes place six times while a crankshaft rotates twice. Accordingly, the general supply pump 2 feeds the fuel six times while the crankshaft rotates twice, with the fuel feed timing being in synchronization with the fuel injection timing. However, if it is possible to maintain the common rail pressure to a substantially constant value and insure an appropriate fuel injection, the supply pump 2 does not have to feed the fuel six times.
In consideration of the foregoing, a supply pump may be designed not to feed the fuel to the common rail in synchronization with the fuel injection timing. Specifically, the number of fuel delivery to the common rail 3 from the supply pump 2 during two rotations of the engine crankshaft 78 may differ from the number of the cylinders of the engine 86. For instance, a supply pump originally designed for a four-cylinder engine may be used in a six-cylinder engine. If this combination is feasible, a manufacturing cost will be reduced since the same supply pump is applicable to both of the four- and six-cylinder engines.
However, an excessively large load acts on the drive power transmission mechanism 84 between the supply pump 2 and the engine 86 unless the fuel delivery timing is optimum. In other words, if the timing of fuel supply from the supply pump is not appropriate, a chain tension and the like become so large, and therefore the same supply pump is not usable in different engines.
One object of the present invention is to provide a supply pump for a common rail fuel injection system, that is able to optimize a fuel delivery timing and therefore reduce a load on a drive power transmission mechanism.
Another object of the present invention to provide a supply pump for a common rail fuel injection system, that is applicable to an engine, the number of cylinders of which engine is different from the number of fuel delivery per two rotations of a crankshaft.
According to one aspect of the present invention, there is provided a supply pump for a common rail fuel injection system, which is driven by a multi-cylinder engine via a power transmission mechanism to feed a pressurized fuel to a common rail from the supply pump, characterized in that the number of fuel delivery to the common rail from the supply pump per two rotations of a crankshaft of the engine is different from the number of cylinders of the engine, and the fuel delivery timing is determined such that a less load acts on the power transmission mechanism.
According to another aspect of the present invention, there is provided a supply pump for a common rail fuel injection system, which is driven by a multi-cylinder engine via a power transmission mechanism, characterized in that the number of fuel delivery to a common rail from the supply pump per two rotations of an engine crankshaft is different from the number of engine cylinders, and a reference fuel delivery end timing is set to 30xc2x0xc2x15xc2x0 after a compression top dead center of a reference cylinder in terms of crankshaft angle and subsequent fuel delivery end timings come at constant intervals. The constant intervals are determined by dividing 720xc2x0 by the number of fuel delivery.
In one preferred example of the present invention, the number of fuel delivery is four and the number of engine cylinders is six. These six cylinders may be called #1 cylinder, #2 cylinder . . . and #6 cylinder from the above-mentioned xe2x80x9creference cylinderxe2x80x9d in the order of compression. The first or reference fuel delivery end timing may be 30xc2x0 after compression top dead center of #1 cylinder, the second fuel delivery end timing may be 30xc2x0 before compression top dead center of #3 cylinder, the third fuel delivery end timing may be 30xc2x0 after compression top dead center of #4 cylinder and the fourth fuel delivery end timing may be 30xc2x0 before compression top dead center of #6 cylinder. The multi-cylinder engine may be a so-called V-6 engine. The drive power transmission mechanism may be a chain-and-sprocket mechanism.
The supply pump may include a pump shaft driven by the engine via the drive power transmission mechanism, a feed pump driven by the pump shaft, a plunger chamber for receiving a fuel from the feed pump and having a plurality of radiantly extending channels, a plurality of plungers slidably placed in the plurality of plunger chamber channels respectively such that they are biased in radially outward directions of the plunger chamber respectively by the fuel received in the plunger chamber, a cam surface formed on an inner surface of the pump shaft for surrounding the plunger chamber to restrict reciprocating movements of the plungers in radial directions of the plunger chamber, cam projections formed on the cam surface for forcing the plungers in radially inward directions of the plunger chamber upon rotations of the pump shaft to supply the fuel to the common rail from the plunger chamber, a fuel passage connecting the feed pump to the plunger chamber, and a flow rate control valve located in the fuel passage for regulating an amount of fuel to be introduced to the plunger chamber thereby controlling an amount of fuel to be supplied to the common rail.
The plunger chamber may have four channels extending radiantly like a xe2x80x9cXxe2x80x9d shape from a center of the plunger chamber, and four plungers may be received in these channels respectively. The supply pump may stop the fuel delivery when the plungers are moved to the most radially inward position. The fuel delivery timing may not be synchronous to the fuel injection timing.
According to still another aspect of the present invention, there is provided a supply pump for a common rail fuel injection system, which is driven by a multi-cylinder engine via a drive power transmission mechanism, characterized in that the number of engine cylinders is equal to a multiple of the number of fuel deliver per two rotations of engine crankshaft and an integer, and fuel delivery takes place while an engine revolution speed is dropping due to compression strokes of particular engine cylinders.
The engine revolution speed dropping range in terms of crankshaft angle may be between 60xc2x0 before compression top dead center of a predetermined cylinder and 15xc2x0 after the compression top dead center. The number of fuel delivery may be three, the integer may be two and the number of engine cylinders may be six. The fuel delivery start timing may be between 60xc2x0 before compression top dead center of the predetermined cylinder and the compression top dead center, and the fuel delivery end timing may be between 15xc2x0 before compression top dead center of the predetermined cylinder and 15xc2x0 after the compression top dead center. The six cylinders of the engine may be called #1 cylinder, #2 cylinder . . . and #6 cylinder in the order of compression. The xe2x80x9cpredetermined cylinderxe2x80x9d may be #1, #3 and #5 cylinders. The multi-cylinder engine may be a so-called V-6 engine. The drive power transmission mechanism may be a chain-and-sprocket mechanism.
The supply pump may include a pump casing, a pump shaft driven by the engine via the drive power transmission mechanism and rotatably supported in the pump casing, a feed pump driven by the pump shaft, a plunger chamber for receiving a fuel from the feed pump and having a plurality of channels extending radiantly from a center of the plunger chamber, a plurality of plungers slidably placed in the channels of the plunger chamber respectively such that they are biased in a radially outward direction of the plunger chamber by the fuel received in the plunger chamber, a means for restricting reciprocating movements of the plungers in a radial direction of the plunger chamber, a cam means for moving the plungers in a radially inward direction of the plunger chamber upon rotations of the pump shaft to supply the fuel to the common rail from the plunger chamber, a fuel passage connecting the feed pump to the plunger chamber, and a flow rate control valve located in the fuel passage for regulating an amount of fuel to be introduced to the plunger chamber thereby controlling an amount of fuel to be supplied to the common rail. The pump shaft may have a hollow portion to define an inner surface, and the restriction means may be this inner surface of the pump shaft that surrounds the plunger chamber. The cam means may be cam projections formed on the inner surface of the pump shaft for moving the plungers in a radially inward direction of the plunger chamber upon rotations of the pump shaft. The plunger chamber may have three channels extending radiantly in a xe2x80x9cYxe2x80x9d shape from a center of the plunger chamber and three plungers may slidably be received in the three channels respectively. The supply pump may stop fuel delivery when the plungers move to the most radially inward position. The fuel delivery timings may be synchronous to fuel injection timings. The supply pump may start the fuel delivery between 120xc2x0 before compression top dead center of a predetermined cylinder and the compression top dead center, and may terminate the fuel delivery between 15xc2x0 before compression top dead center of the predetermined cylinder and 15xc2x0 after the compression top dead center.